Method and apparatus for sealing centrifuge tubes

Abstract

A method of closing or sealing a filler passage formed in a neck or stem protruding from the small access opening in the upper end of a substantially closed centrifuge tube. The neck is formed of a readily fusible material and a heat conductive cap member is positioned over the open end portion of the neck closely confining it therein. Heat and pressure are applied to the cap causing progressive portions of the neck to melt and fold into the filler passage where it forms a molten mass within the filler passage above the access opening to the tube. Heat and pressure are removed, permitting the cap to cool and the molten mass to solidify completely sealing or filler passage of the centrifuge tube. The cap is then removed and the centrifuge tube is fully prepared for centrifugation.

What is claimed is: 
     
       1. A method for closing a filler passage formed in a neck protruding from the opening in the end of a substantially closed centrifuge tube, the neck being formed of a heat fusible material, comprising: supporting said centrifuge tube in an upright position with said filler neck protruding upwardly;   placing a heat conductive cap over the open end portion of said neck, said cap having an inner cavity closely confining the outer surface of the end portion of said neck therein;   applying heat to said heat conductive cap sufficient to melt the confined end portion of said neck;   applying pressure to said cap moving said cap in a direction along the longitudinal axis of said neck thereby causing progressive portions of said neck to melt and fold inwardly into the filler passage therein;   removing said heat and pressure from said cap so that said cap cools and the melted material in said filler passage of said neck solidifies therein completely closing said filler passage; and   removing said cap from said neck.   
     
     
       2. The method defined in claim 1 wherein said cap is heated by means of a heating element which supplies heat to said cap and also applies pressure on said cap in a direction along the axis of said neck. 
     
     
       3. The method defined in claim 1 in which said cap has an inwardly slanting wall surface forcing said melting portion of said neck to fold inwardly as pressure is applied to said cap in a direction along the longitudinal axis of said neck. 
     
     
       4. The method defined in claim 1 in which said cap has a hemispherical shaped inner cavity surface forcing said melting portions of said neck to fold inwardly. 
     
     
       5. The method defined in claim 1 in which heat is applied by means not engaging said cap and the pressure applied in a direction along the longitudinal axis of said neck comprises the weight of the cap. 
     
     
       6. The method defined in claim 1 in which heat is applied to said cap prior to its placement over the open end portion of said neck and pressure and heat are then applied until the end portions of said neck melt wherein said heat and pressure are removed from said cap. 
     
     
       7. The method defined in claim 1 including the step of applying external cooling means in contact with said heat conductive cap after said heat and pressure are removed in order to quickly cool said cap and solidify the melted material in said filler passage. 
     
     
       8. A method for closing a filler neck protruding from the opening in the end of a substantially closed centrifuge tube, the filler neck being formed of a heat fusible plastic material and having a filler passage along the axis of said neck for delivery of liquid into the centrifuge tube, comprising: supporting said centrifuge tube in an upright position with said filler neck protruding upwardly;   placing a heat conductive cap over the open end portion of said neck, said cap having an inner cavity closely confining the outer surface of the end portion of said neck therein;   applying heat to said heat conductive cap sufficient to melt the plastic material forming the confined end portion of said neck;   applying pressure to said cap moving said cap in a direction along the longitudinal axis of said neck thereby causing progressive portions of said neck to melt and fold inwardly to form a mass of plastic material in said filler passage;   supporting said neck at some position above the centrifuge tube while said heat and pressure are applied to said neck above such position in order to maintain said neck oriented in an upward direction;   removing said heat and pressure from said cap so that said cap cools and said mass of melted plastic material in said filler passage solidified therein completely closing said filler passage; and   removing said cap from said neck.   
     
     
       9. A method for closing a filler neck protruding from the opening in the end of a substantially closed centrifuge tube, the neck being formed of a heat fusible plastic material and having a filler passage along the axis of said neck for delivery of liquid into the centrifuge tube, comprising: supporting said centrifuge tube in an upright position;   applying a clamping means to support said filler neck at a predetermined position above said centrifuge tube thereby maintaining said neck in a substantially upright position;   placing a heat conductive cap over the open end portion of said neck, said cap having an inner cavity closely confining the outer surface of the end position of said neck therein;   applying heat to said heat conductive cap sufficient to melt the confined end portion of said neck;   applying pressure to said cap moving said cap in a direction along the longitudinal axis of said neck thereby causing progressive portions of said neck to melt and fold inwardly to form a mass of plastic material closing said filler passage, said pressure forcing said cap along said neck until lower portions thereof abut against said clamping means;   removing said heat and pressure from said cap so that said cap cools and said mass of plastic material in said filler passage solidifies to close said filler passage; and   removing said cap and said clamping means from said neck.   
     
     
       10. The method defined in claim 9 including the additional step of applying external cooling means to said cap after said heat and pressure are removed in order to quickly cool said cap and solidify the mass of melted plastic closing said filler passage. 
     
     
       11. Apparatus for closing a passage formed in a filler neck protruding from the opening in the end of a substantially closed centrifuge tube after said tube has been filled with sample, the neck being formed of a heat fusible material, comprising: means adapted to engage the outer surface of said centrifuge tube for supporting said centrifuge tube in an upright position with said filler neck protruding upwardly;   a cap formed of a high heat conductivity material having a cavity adapted to closely fit the circumference of said filler neck, said cap adapted to be positioned over the end portion of said filler neck to confine said end portion of said neck within said cavity;   means for applying heat to said cap member for raising the temperature thereof to the fusion temperature of said material forming said neck;   pressure applying means movable upwardly and downwardly in a direction subsantially along the axis of said filler passage, said pressure applying means adapted to apply pressure downwardly against said cap so that, when said cap is heated to the fusion temperature of said neck, progressive portions of said neck melt and said cap is forced downwardly so that the sidewalls of said filler neck fold inwardly into said filler passage and form a molten mass closing said filler passage;   clamping means adapted to grasp said neck at some predetermined position above the upper end of said centrifuge tube to maintain said neck in a substantially upright position as pressure and heat are applied to said cap; and   means for retracting said pressure applying means and interrupting said heat applying means thereby permitting said cap to cool and said molten mass to solidify within the filler passage of said neck of said centrifuge tube.   
     
     
       12. The apparatus of claim 11 in which said pressure applying means is also a heating element for supplying both pressure and heat to said heat conductive cap. 
     
     
       13. The apparatus defined in claim 11 in which said cap is formed of aluminum. 
     
     
       14. The apparatus defined in claim 11 in which said cap comprises a central section defining a hemispherical shaped cavity and includes a cylindrical sidewall to encompass the outer circumference of said neck and support said cap on said filler neck without external supporting means. 
     
     
       15. The apparatus defined in claim 14 in which said cap further includes a rim of low heat conductive material attached to the bottom portion of the cylindrical sidewall thereby providing a heat insulating means between the centrifuge tube and the heat conductive portions of said cap. 
     
     
       16. The apparatus defined in claim 15 in which said low heat conductive rim is formed of titanium or ceramic material and includes a lower surface and shoulder conforming to the upper surface of said centrifuge tube at its connecting point with said neck. 
     
     
       17. Apparatus for closing a passage formed in a filler neck protruding from the opening in the end of a substantially closed centrifuge tube after said tube has been filled with sample, the neck being formed of a heat fusible material, comprising: means adapted to engage the outer surface of said centrifuge tube for supporting said centrifuge tube in an upright position with said filler neck protruding upwardly;   a cap formed of high heat conductivity material having a cavity adapted to closely fit the circumference of said filler neck, said cap adapted to be positioned over the end portion of said filler neck to confine said end portion of said neck within said cavity;   means for applying heat to said cap member for raising the temperature thereof to the fusion temperature of said material forming said neck;   pressure applying means movable upwardly and downwardly in a direction substantially along the axis of said filler passage said pressure applying means adapted to apply pressure downwardly against said cap so that, when said cap is heated to the fusion temperature of said neck, progressive portions of said neck melt and as said cap is forced downwardly the side-walls of said filler neck fold inwardly into said filler passage and form a molten mass closing said filler passage,   clamping means adapted to grasp said neck at some predetermined position above the upper end of said centrifuge tube to maintain said neck in a substantially upright position as pressure and heat are applied to said cap;   means for retracting said pressure applying means and interrupting said heat applying means from said cap; and   cooling means movable into contact with said cap for rapidly cooling said cap and permitting said molten mass to solidify thereby closing the filler passage in said neck of said centrifuge tube.   
     
     
       18. The apparatus defined in claim 17 in which said cooling means comprises a strip of copper or other high thermal conductivity material placed into contact with the upper portion of said cap to provide a heat sink for rapidly conducting heat from the cap. 
     
     
       19. The apparatus of claim 12 in which there is provided on said heating element a cap retainer for supporting said cap on said heating element for heating said cap prior to its engagement with the end portion of said neck and including means for releasing said cap when said heating element is withdrawn.